The present invention relates to a method of measuring the adhesive strength of polymers interfaces. More particularly, the present invention is directed to a method of measuring the adhesive strength of polymers interfaces in a combinatorial manner.
The adhesion strength (or weakness) of polymeric materials is a critical property for numerous technologies. For example, in electronic packaging, polymeric materials are used as thermal insulator layers, electrical insulator layers, or as binders between two non-adhesive material layers. In each of these cases, the mechanical integrity of the resulting electronic package is directly dependent upon the integrity of the polymer interfacial areas. Therefore, the surface properties as well as the bulk properties of the polymer layers must be properly chosen and/or engineered to maximize or achieve a desired or required degree of adhesion strength for a given environment of a particular electronic package. In some applications, minimizing the adhesive properties of polymer layers may be required rather that maximizing the adhesive properties. An example of the latter application is a biomedical device that is required to be resistant to contamination. One method of controlling contamination of such biomedical devices is to use a properly engineered polymer coating that minimizes the adhesion between the polymer and common, targeted or suspected contaminants. This process of minimizing the adhesion between the polymer and common, targeted or suspected contaminants must be performed so that the adhesion is at the same time optimized for the operating conditions or environment of the biomedical devices.
Given the wide range of physical requirements and end-use environmental conditions, finding an optimal polymer, i.e., one that has or can be engineered to have desired or required adhesive properties for a particular substrate, can be a difficult, time consuming task, since a reliable theory for general polymer interfacial strength does not exist. The efficiency of finding the best polymer material(s) is ultimately limited by the inefficiency of existing adhesion tests. These adhesion tests are not only inefficient, but the results of many of them are unreliable.
Many companies such as Symyx Technologies of Santa Clara, Calif. are developing instruments to use combinatorial methods to aid in materials discovery and characterization. For example U.S. Pat. No. 6,030,917 to Weinberg et al. discloses methods and apparatus for screening catalysts. U.S. Pat. No. 6,175,409 to Nielsen et al discloses flow-injection analysis and variable-flow light-scattering methods and apparatus for characterizing polymers. U.S. Pat. No. 6,182,499 to McFarland et al. discloses systems and methods for characterization of materials and combinatorial libraries with mechanical oscillators. U.S. Pat. No. 6,157,449 to Hajduk discloses depolarized light scattering array apparatus and methods of using the same. Although these U.S. Patents address properties and techniques that are important for the development of polymer technologies and demonstrate the growing interest in combinatorial measurement techniques, they do not provide a method for characterizing properties that are directly related to the adhesive strength of polymer interfaces.
U.S. Pat. No. 5,477,732 to Yasue e al., U.S. Pat. No. 4,137,761 to Miller, U.S. Pat. No. 5,144,845 to Pyke, U.S. Pat. No. 3,548,652 to Beatty et al., and U.S. Pat. No. 4,194,392 to Lombard et al exemplify various techniques and instruments that have been developed for measuring polymer adhesion. Each of the techniques disclosed in these patents makes a quantitative measurement of the adhesive strength of a polymer interface. However, the measured quantities are only truly useful as relative measures of adhesion and therefore, the measurements from these techniques cannot be correlated with physical properties of the contacting materials.
To make quantitative, absolute measurements of adhesive strength, more laborious techniques are commonly used. Two accepted techniques for these measurements include the flat punch probe tack test (ASTM 15.06; Creton, 2000) and the spherical probe, or JKR, technique (Johnson et al, 1971). Both probe techniques provide very quantitative measurements of polymer adhesion by using a single probe (either a flat punch or a spherical punch) to mechanically form and separate a polymer interface in a single test. Using fracture mechanics relations and the measured quantities of force and contact area or displacement and contact area, the adhesion energy of the interface can be quantified. Although accurate and quantitative, the efficiency of these procedures is limited due to the required analysis and the total time to complete a single test.
No existing technologies provide a means of conducting combinatorial investigations of polymer adhesion.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a method of measuring the adhesive strength of a polymer which involves:
providing a lens array having a plurality of individual lens elements on a surface thereof;
providing a substrate;
applying a polymer to at least one of the individual lens elements of the lens array or the substrate;
contacting the individual lens elements of the lens array with the substrate;
separating the lens array and substrate from one another while monitoring changes in contact area of the individual lens elements; and
calculating the adhesive strength of the polymer at the contact area.
The present invention further provides a method for measuring the adhesive strength of polymer material interfaces that are arranged in a combinatorial library which involves:
providing a lens array having a plurality of individual lens elements on a surface thereof;
providing a substrate;
contacting the individual lens elements of the lens array with the substrate in a controlled manner while providing a parameter gradient there between and monitoring changes in contact area, said parameter gradient comprising at least one of a physical parameter, an environmental parameter and a material parameter; and
calculating the adhesive strength of the polymer at the contact area.